Harold Hall

Workshop Processes

The calculation has to be carried out at each position that the infeed is changed
and from the same baseline, see Sk. 4

Initially, I chose to make the changes in diameter at 1/8" increments, being one
turn of my lathe's leadscrew. This resulted in quite large steps at the smaller end
and I finally opted for 1/16" increments, half a turn of the leadscrew, resulting
in 26 increments. A benefit of this choice was that as precision was not required
it was unnecessary to read the micrometer dials just observe the position of the
handle on the hand wheel, typically up and down.

Viewers will no doubt be interested in my method for avoiding the lengthy process
of manually calculating the twenty-six tool infeed values. Actually, purely out of
interest, I tried two methods. First, using my CAD system, see Sk. 5, I
drew actual size the distance between the two extremities X and Z and positioned
point Y (B). Using these three points I asked the system to draw a circle based on
these (C) and from this called up the resulting radius. It was satisfying to find
that even when calling up the value to 8 decimal places the result was identical
to the calculated value.

I then drew a vertical line tangent to the peak of the curve, being the zero point
for the tool in its starting position and drew horizontal lines at each of the 26
infeed positions, (D). These lines were then trimmed to the vertical straight and
curved lines (E). With that done I chose a typical position and requested the length
of the line, manually calculating this value also. Again, I found both values identical
even at 8 decimal places. I have though exaggerated the curve and reduced the number
of points on the sketch to make the drawing more easily read.

My CAD system has a database facility but I have never found the need to conquer
it and this was also not the time to attempt this. As a result, I would have to select
each line individually and write down the values as a list. Because of this, I resorted
to my favourite method where repeated calculations have to be made, that is using
a spread sheet.

It would not be appropriate to discuss spread sheets in detail for this process item
but their major advantage is, over say a programmable calculator, or a CAD program,
the ability to obtain a print out that can be used away from the computer, typically,
in the workshop. Also, where only a limited number of values require imputing (HV,
IVD and VD in this case) these can be changed and other sets of values obtained almost
instantaneously, more about that to finish with.